1. Field of the Invention
The present invention relates to a bump forming method for forming solder bumps that are intended to serve as mechanical and electrical connecting terminals, a method of conducting preliminary treatment before soldering (hereinafter called presoldering treatment) technically associated with said bump forming method, a soldering method grown from said presoldering treatment method, and apparatuses for employing these methods, such as a bump forming apparatus, a presoldering treatment apparatus and a soldering apparatus.
2. Discussion of the Related Art
Conventionally, a bare chip or a similar component having undergone a fine processing is packaged in such a way as to be easily mounted on a printed circuit board. The most typical example of such components are semiconductors. It has heretofore been common practice that an electrode pad portion of a bare chip is connected to an inner lead portion of a lead frame by a wire and sealed with a resin or ceramic material and that an outer lead portion extending to the outside of the chip serves as a mechanical and electrical connecting terminal to be connected to the packaging surface of the printed circuit board.
The rapidly increasing need recently to make electronic devices smaller, thinner, and lighter, as well as faster, has also made it necessary for the electronic components to be smaller and faster. For example, there has been an attempt to reduce the pitch between the leads of a Quad Flat Package (QFP), which is a semiconductor package provided with leads at the four sides of the package, from 0.65 mm to 0.4 mm. In order to cope with further reduction in the size of electronic equipment, vigorous efforts are being made to develop area-array packages of surface mount types.
An area array package is a package provided with electrodes that are arranged in a grid on the bottom of the package. Because of planar arrangement of the electrodes instead of a conventional linear arrangement, an area-array package is compact and provided with numerous pins. The design of connecting terminals for connecting an area array package to a printed circuit board has also changed from those attached to the lead frame to protrusion-shaped terminals (bumps) formed on the electrodes.
A change has also occurred in the wiring in a package, which used to be done with electrical wires; what is becoming necessary is flip chip joining using bumps formed on electrode portions. Such a change has been implemented, because the inductance component and other undesirable characteristics of a wire impair reduction of the operating speed and also cause various problems, such as improper functioning which is caused by simultaneous switching noises.
Examples of area array packages include a ball grid array (BGA), which may be used as a substitute for a QFP, and a chip scale package (CSP), which is reduced to a size nearly the same as a chip.
Furthermore, a part of the flip chip attaching (FCA) technique has already been put into practical use.
Terminals attached to the various electronic elements mentioned above are bump-shaped terminals instead of those of the conventional lead frame type. The most widely used are solder bumps, because they can cope with a batch reflow process, which is a part of the typical conventional procedure for production of a printed circuit board.
With regard to the bump forming technique, several methods have heretofore been offered. Those conventional methods are roughly divided into two categories: those using gold wires and those using solder alloys.
Examples of methods using gold wires include the Stud Bump Bonding (SBB) technique offered by Kyushu Matsushita Electric Co., Ltd. (IEMT ""93: pp. 362-365, 1993) and the Press Contact technique offered by NEC Corp. (Mate ""97 Microjoining and Assembly Technology in Electronics: pp. 15-18, 1997).
Both techniques call for a wire bonder to form gold bumps on the electrode side of a bare chip with a gold wire. With regard to connection of the chip to a substrate, the SBB technique calls for connection using silver paste, while the Press Contact technique calls for maintaining contact between the gold bumps and an electrode pad of the substrate solely by the contraction stress of the underfill resin.
Problems common to these techniques are:
(1) it takes too much time to form bumps, because bumps are formed one by one by studding an electrode pad of a bare chip with a gold wire by using a wire bonder;
(2) using expensive gold increases the cost per bump; and
(3) as a batch reflow process with other surface mount components is impossible, each chip has to be individually mounted on a printed circuit board.
The Press Contact technique presents another problem in that a variance or insufficient accuracy in the height of gold bumps and the degree of surface smoothness of substrates have a considerable influence on obtaining reliable electrical connection, in other words the mounting efficiency, and may therefore present a serious problem in the yield of the product.
Regarding methods of using a solder alloy, a typical method calls for forming a solder bump by placing a solder ball having characteristics within standards on an electrode that is mounted on a bare chip and coated with a fusing agent (hereinafter called xe2x80x9cfluxxe2x80x9d), and then conducting a reflow treatment. Solder balls for BGA are already available.
NEC Corp. has also offered a method of forming solder bumps by using the micropunching technique; this method calls for punching out a solder tape, placing solder pieces on an electrode that is mounted on a bare chip and coated with flux, and then conducting reflow treatment (""95 Japan IEMT Symposium: pp. 117-120).
Other examples include a solder paste printing method by Hitachi Techno Engineering Co., Ltd. (Mate ""97 Microjoining and Assembly Technology in Electronics: pp. 19-22) and a plating method by TOSHIBA CORPORATION (Mate ""97 Microjoining and Assembly Technology in Electronics: pp. 23-38).
All of the methods mentioned above call for, in some way or another, placing a solder alloy on an electrode pad and performing reflow to form solder bumps. Flux is always used for the reflow treatment and, thereafter, removed by washing.
In other words, according to any one of the methods of forming solder bumps, flux is indispensable and its washing process is accordingly necessary. Depending on its thoroughness, washing may produce flux residue, which may have a serious influence on the reliability of the finished electronic element.
For this reason, the washing process requires a vigorous cleaner, such as a Freon substitute. In addition to thus necessitating a process that will have an damaging effect on the environment, these methods present a problem of excessively high production costs in their requirement of an expensive facility and disposal of waste liquid.
There have been patent applications relating this field, such as those laid open under Provisional Publication Nos. 293952/1988, 148481/1989 and 500026/1993.
Japanese Patent Provisional Publication No. 293952/1988 describes a method of removing oxides from the surface of solder on an electrode portion by means of hydrogen plasma reduction when the solder is heated and melted in a vacuum.
However, hydrogen reduction damages a passivation film on a bare chip. Furthermore, using hydrogen presents the danger of explosion and requires proper measures to handle the exhaust, resulting in high production costs.
Japanese Patent Provisional Publication No. 148481/1989 describes a method of removing oxides by using argon plasma.
This method, however, is limed to cases of thermal bonding of a flat surface to another flat surface and not applicable to bump formation. Furthermore, a test has proved that treatment using argon plasma is unable to produce good bumps.
The method has another drawback in that the cost of the apparatus is very high, because the initial degree of vacuum in the chamber has to be considerably low: approximately 10xe2x88x925 Torr. Furthermore, in case an oil diffusion pump is used, pollution by the oil will be a problem.
Japanese Patent Provisional Publication No. 500026/1993 describes a method that calls for fluorination of a solder surface by using fluorine-containing plasma in order to remove an oxide film that will impair wetting at the time of solder bonding.
However, fluorine plasma has the property of corroding silicon and a passivation film. Furthermore, silicon tetrafluoride, which is a reaction product, sometimes reacts with solder bumps and consequently damages the solder bumps. Fluorine residue may exert a serious influence on the reliability of the finished product, depending on the residual percentage.
In short, conventional methods that call for use of a gold wire require an excessively long processing period and high production costs and also present a problem in mounting a product on a substrate. Conventional methods using a solder alloy require use of flux and therefore present problems resulting from the postprocess washing. As for conventional methods involving plasma treatment, there is none that is suitable for forming solder bumps.
In order to solve the above problem, an object of the present invention is to provide a bump forming method and a bump forming apparatus for forming solder bumps serving as element electrode terminals that can cope with an electronic element having reduced dimensions. To be more specific, a bump forming method and a bump forming apparatus according to the invention are capable of forming such solder bumps with an inexpensive soft solder alloy and without using flux so that there is no need of postprocess washing and that finished solder bumps will have high reliability. Another object of the invention is to provide a presoldering treatment method and a presoldering treatment apparatus which are also capable of solving the above problems. Yet another object of the invention is to provide a soldering method and a soldering apparatus which are results of development from these methods and apparatuses.
A bump forming method according to the invention is a method of forming solder bumps, which will serve as connecting terminals, on the surface of an object (hereinafter called workpiece) by accumulating a soft solder alloy on the surface of the workpiece; irradiating the accumulated soft solder alloy with at least plasma that contains hydrogen; and applying reflow treatment to the soft solder alloy that has been irradiated with at least said plasma that contains hydrogen.
As hydroxides and oxides in the soft solder alloy are removed by irradiation of the accumulated soft solder alloy with hydrogen-containing plasma, bumps that will serve as mechanical and electrical connecting terminals are formed without the need of flux during the reflow treatment.
A bump forming method according to another feature of the invention is similar to the bump forming method described above and further characterized in that the reflow treatment and the hydrogen-containing plasma irradiation are conducted in a vacuum either simultaneously or with the reflow treatment following immediately after the hydrogen-containing plasma irradiation.
As a result, the quality of the product and the productivity can be increased. Conducting reflow treatment in a vacuum is especially effective in preventing re-oxidation of the soft solder alloy during the reflow. Conducting reflow treatment in a vacuum either simultaneously with or immediately after plasma irradiation enables the increase of the quality of the product and the productivity.
A bump forming method according to yet another feature of the invention is similar to either bump forming method of the invention described above and further characterized in that it calls for conducting the reflow treatment in either an inert gas atmosphere, such as a nitrogen atmosphere, or a reductive atmosphere.
As a result of this feature, the method is capable of preventing re-oxidation of the soft solder alloy during the reflow, thereby increasing the quality of the product.
A bump forming method according to yet another feature of the invention is similar to any one of the bump forming methods of the invention described above and further characterized in that it calls for irradiating the soft solder alloy with hydrogen-containing plasma at a temperature lower than the melting point of the soft solder alloy, the range of permissible temperature including room temperature.
As a result of this feature, the method is capable of clearly separating the process of plasma treatment to the soft solder alloy from the reflow process and ensuring proper execution of each process.
A bump forming method according to yet another feature of the invention is similar to any one of the bump forming methods of the invention described above and further characterized in that the process gas for generating the hydrogen-containing plasma is a mixed gas containing an inert gas and hydrogen gas that contains hydrogen with a mixing ratio of equal to or more than 3 V/V % but less than 8 V/V % calculated in terms of hydrogen molecules.
By using a mix that has been prepared by separately feeding an inert gas and either hydrogen gas or hydrogen-containing gas, or using a premixed gas, plasma irradiation is conducted. Using a process gas that is a mixed gas comprised of an inert gas to which hydrogen gas is added with a mixing ratio of equal to or more than 3 V/V % but less than 8 V/V % with respect to the total volume of the mixed gas not only achieves high plasma treatment effect (spattering effect) but is also desirable in view of safety, costs and other factors. Limiting the hydrogen content to not less than 3 V/V % ensures removal of hydroxides and oxides from the soft solder alloy, while limiting the hydrogen content to less than 8 V/V % ensures the safety and eliminates the need of treatment of exhaust gas.
Our tests have clearly proved that adding an excessive quantity of hydrogen to argon gas causes its plasma to selectively and severely etch a certain potion of the solder structure, i.e. the portion rich in tin, resulting in damage to the surface of the solder bumps. Therefore, it is desirable to limit the quantity of the hydrogen added to less than 10%.
A bump forming method according to yet another feature of the invention is similar to any one of the bump forming methods of the invention described above and further characterized in that the duration of the plasma irradiation is limited to less than two minutes. By plasma irradiation for less than two minutes, the method is capable of giving the soft solder alloy a sufficient quality improving treatment, thereby forming good solder bumps, and protecting the workpiece from possible damage.
A bump forming method according to yet another feature of the invention is similar to any one of the bump forming methods of the invention described above and further characterized in that the reflow treatment is conducted by means of heat radiation in a vacuum. By using heat radiation, the method ensures the effective reflow heating in a vacuum.
A bump forming method according to yet another feature of the invention is similar to any one of the bump forming methods of the invention described above and further characterized in that irradiation with fluorine-containing plasma is performed after irradiation with the hydrogen-containing plasma.
Because of this feature, the method is capable of limiting possible damage to a passivation film, which is a protective coat for a microcircuit formed on such a workpiece as a silicone wafer. For example, the method is capable of reducing etching of silicon oxide, silicon nitride, etc. or ashing of organic coats.
A bump forming method according to yet another feature of the invention is similar to the bump forming method described above and further characterized in that the fluorine-containing plasma contains either one of or both argon and oxygen.
Because of the fluorine-containing plasma irradiation conducted after the irradiation with the hydrogen-containing plasma, the method is capable of reducing the duration of the surface treatment and limiting damage to a passivation film.
A bump forming method according to yet another feature of the invention is similar to the bump forming method described above and further characterized in that the duration and the temperature of irradiation with fluorine-containing plasma are respectively limited to within 60 seconds and a temperature lower than the melting point of the soft solder alloy, the range of permissible temperature including room temperature.
By thus limiting the duration and the temperature of irradiation with fluorine-containing plasma, the method enables the quick surface treatment and the reduction of damage to passivation films.
A bump forming method according to yet another feature of the invention is similar to any one of the bump forming methods of the invention described above and further characterized in that the workpiece is preheated at a temperature not higher than 100xc2x0 C. when conducting the reflow process.
As a result, it is possible to prevent the quality of the surface of the workpiece that has undergone surface treatment process from changing during the reflow process. Therefore, the method is capable of improving bonding between the bonding surfaces of the two objects where they are bonded to each other.
A bump forming method according to yet another feature of the invention is similar to any one of the bump forming methods of the invention described above and further characterized in that irradiation with hydrogen-containing plasma is performed again after the reflow process.
By performing plasma irradiation also after the reflow process, the minimal quantity of oxides or other impurities that appeared on the surface of the solder during the melting of the solder are removed. The method is thus capable of forming bumps that have cleaner surface.
A soldering method according to the present invention is a method that calls for bringing the soft solder alloy on the surface of a workpiece into contact with the surface of a bonding target, i.e. an object to which said workpiece is intended to be soldered, and thus bonding the surface of the workpiece to the surface of the bonding target by soldering during the reflow process of any one of the bump forming methods of the invention described above.
By thus bringing the surface of the soft solder alloy on the surface of the workpiece that has undergone surface reforming treatment into contact with the surface of the bonding target and heating them in the reflow process, the method enables the formation of bumps and bonding the workpiece and the bonding target together by soldering without using flux which would otherwise require post process washing.
A solder bump forming apparatus according to the present invention is adapted to use a soft solder alloy on the surface of a workpiece to form solder bumps, which will serve as connecting terminals, and includes a plasma generating means adapted to generate at least hydrogen-containing plasma under a low pressure; a gas supply means for feeding process gas to the plasma generating means; a workpiece exposing means for exposing the soft solder alloy on the surface of the workpiece at least to hydrogen-containing plasma; and a heating means for applying a reflow treatment the soft solder alloy in a vacuum.
By irradiating the soft solder alloy of the workpiece with hydrogen-containing plasma using the plasma generating means for generating hydrogen-containing plasma, the gas supply means for feeding process gas and the workpiece exposing means for exposing the workpiece to the hydrogen-containing plasma, the apparatus is capable of removing hydroxides and oxides from the soft solder alloy. Furthermore, by conducting the reflow process in a vacuum by the heating means, the apparatus is capable of preventing re-oxidation of the soft solder alloy during the reflow process.
A bump forming apparatus according to another feature of the invention is an apparatus as the bump forming apparatus described above, wherein the plasma generating means is provided with a high frequency power supply and an electrode for generating plasma, said electrode connected to the high frequency power supply and having a hollow electrode body adapted to receive the process gas, supply openings that are adapted to feed the process gas and bored in the end of the electrode body facing away from the workpiece, and through holes bored through the electrode body so as to extend from the end where the supply openings are formed to the opposite end.
Because of the structure described above, plasma ions generated from the process gas ejected from the supply openings, which are located opposite the workpiece, can be trapped and removed by the through holes, which serve as H tunnels for trapping plasma ions when the ions pass the through holes. By thus preventing a violent collision of ions with the workpiece, the apparatus is capable of protecting a passivation film or other parts of the workpiece from damage that is prone to be caused by hard, physical etching resulting from collision with ions. Meanwhile, active species that etch, when in the excited state, the workpiece through soft, chemical reaction are allowed to pass through the through holes and thus effectively utilized.
A bump forming apparatus according to yet another feature of the invention is an apparatus similar to either bump forming method of the invention described above and further characterized in that the heating means has a light source, which is adapted to heat the backside of the workpiece by radiation, and a reflecting mirror for adjusting luminous flux from the light source.
As a result of the structure that calls for heat radiation with the luminous flux from the light source adjusted by the reflecting mirror, the apparatus is capable of quick, intensive heating of the workpiece in a vacuum as well as easy temperature control.
A bump forming apparatus according to yet another feature of the invention is an apparatus as any one of the bump forming apparatuses of the invention described above and further characterized in that the apparatus includes a gas recovery means that defines the flow of the gas that carries plasma generated between said electrode and another electrode to the workpiece, said gas recovery means disposed such that the workpiece is positioned between the gas recovery means and the gas supply means.
As a result of the structure wherein the flow of the gas for carrying plasma or radicals (active species) generated between the aforementioned electrode and another electrode to the workpiece is defined by the gas supply means and the gas recovery means, which is disposed such that the workpiece is positioned between the gas recovery means and the gas supply means, the apparatus is capable of plasma irradiation with an increased efficiency.
A bump forming apparatus according to yet another feature of the invention is an apparatus as any one of the bump forming apparatuses of the invention described above and further characterized in that the heating means includes a light source and a reflecting mirror, said light source disposed at such a location so as not to be exposed to plasma and adapted to heat the workpiece by radiation, and said reflecting mirror adapted to form an optical path extending from the light source to the workpiece.
As a result of the structure described above, the apparatus is capable of preventing the plasma from inflicting damage to the light source or other components and also from causing chemical reduction.
A bump forming apparatus according to yet another feature of the invention is an apparatus as any one of the bump forming apparatuses of the invention described above and further characterized in that the apparatus includes a gas supply means for supplying a process gas, which is a mixed gas containing an inert gas and hydrogen gas that contains hydrogen with a mixing ratio of equal to or more than 3 V/V % but less than 8 V/V % calculated in terms of hydrogen molecules.
A gas containing hydroxyl groups is desirable to be used as the process gas. Taking such factors as the safety, costs and the like into consideration, a mixed gas comprised of an inert gas and hydrogen gas is most suitable. In view of effectiveness of the treatment, a mixed gas comprised of an inert gas to which hydrogen gas is added with a mixing ratio of equal to or more than 3% but less than 8% to the total volume of the mixed gas is particularly desirable. Limiting the hydrogen content to not less than 3 V/V % ensures the highly effective plasma treatment which is capable of effective removal of hydroxides and oxides from the soft solder alloy. Limiting the hydrogen content to less than 8 V/V % ensures the safety and eliminates the need of treatment of exhaust gas.
A bump forming apparatus according to yet another feature of the invention is an apparatus as any one of the bump forming apparatuses of the invention described above and further characterized in that the apparatus includes a high frequency power supply having a frequency of either 13.56 MHz or 2.45 GHz.
The process gas is excited and plasmatized by a 13.56 MHz or 2.45 GHz high frequency power supply, which is inexpensive and easily available.
A bump forming apparatus according to yet another feature of the invention is an apparatus as any one of the bump forming apparatuses of the invention described above and further characterized in that the plasma generating means is adapted to generate fluorine-containing plasma in addition to the aforementioned hydrogen-containing plasma, said fluorine-containing plasma containing either one of or both argon and oxygen.
As a result, the apparatus is capable of reducing possible damage to a protective coat formed on the workpiece and reforming the surface of such a protective coat. Therefore, the apparatus is more suitable for soldering and capable of bonding the soft solder alloy on the workpiece to the surface of the bonding target with increased reliability.
A soldering apparatus according to the invention includes a bump forming apparatus as any one of the bump forming apparatuses of the invention described above; a positioning means for aligning and bringing the soft solder alloy on the surface of a workpiece that has been exposed to plasma and the surface of a bonding target into contact with each other; and a heating means for applying reflow treatment to the film of the soft solder alloy, thereby soldering the surface of the workpiece and the surface of the bonding target together.
Therefore, by aligning and bringing the workpiece that has been treated with plasma and the bonding target into contact with each other by means of the positioning means and conducting a reflow process of the film of the soft solder alloy with the heating means, the soldering apparatus described above is capable of simultaneously performing both the bump forming process and the soldering process without using flux, use of which would necessitate postprocess washing.
A bump forming method according to yet another feature of the invention is a method of forming bumps, which will serve as connecting terminals, on the surface of a workpiece by following the procedure that comprises steps of roughening the surface of a soft solder alloy accumulated on the surface of the workpiece; giving the roughened surface of the soft solder alloy surface reforming treatment that calls for forming a fluorine containing layer on the surface of the soft solder alloy; and applying reflow treatment to the soft solder alloy that has undergone the surface reforming treatment.
A presoldering treatment method according to the invention is a pretreatment method that is intended to be performed prior to soldering of a workpiece and calls for roughening the surface of solder bumps of a soft solder alloy formed on the workpiece, and applying surface reforming treatment to the surface of the solder bumps by forming a fluorine containing layer on the roughened surface of the solder bumps.
A soldering method according to yet another feature of the invention is a method of bonding together a plurality of workpieces by soldering, said soldering method comprising the steps of roughening the surface of solder bumps of a soft solder alloy formed on one or more workpieces and applying surface reforming treatment to the surface of the solder bumps by forming a fluorine containing layer on the roughened surface of the solder bumps; and bringing said one or more workpieces having the solder bumps that have undergone the surface roughening treatment and the surface reforming treatment into contact with other workpiece or workpieces and, in this state, performing reflow of these workpieces. In this case, it does not matter whether any number of the said other workpieces have solder bumps that have undergone the surface roughening treatment and the surface reforming treatment.
The bump forming method, the presoldering treatment method and the soldering method described above are capable of preventing damage to a chip, a circuit board or the like by roughening the surface of the soft solder alloy and accordingly reducing the duration of the surface reforming treatment following the surface roughening treatment. Furthermore, because a fluorine containing layer formed as a result of surface reforming treatment provides increased solder wettability and prevents re-oxidation of the surface of the solder, there is no need of flux to conduct a reflow process or a postprocess washing process.
The surface roughening treatment in any one of the bump forming method, the presoldering treatment method and the soldering method described above is performed by using plasma excitation of an inert gas to which hydrogen has been added.
The quantity of the hydrogen added for said surface roughening treatment ranges from equal to or more than 3 V/V % to less than 8 V/V %.
Argon is used as the inert gas for said surface roughening treatment.
The surface reforming treatment in any one of the bump forming method, the presoldering treatment method and the soldering method described above is performed by using plasma excitation of a mixed gas which contains a fluorine compound or fluorine compounds, and to which either one of or both oxygen and argon are added.
The fluorine compound for said surface reforming treatment consists of at least one of the compounds selected from among carbon fluoride compounds, sulfur hexafluoride and nitrogen trifluoride.
A bump forming apparatus according to yet another feature of the invention includes a surface roughening device for roughening the surface of a soft solder alloy accumulated on a workpiece; a surface reforming device for performing surface reforming treatment by forming a fluorine containing layer on the roughened surface of the soft solder alloy; and a thermal melting unit for performing reflow of the soft solder alloy having the reformed surface, thereby forming solder bumps, which will serve as connecting terminals, on the surface of said workpiece.
A presoldering treatment apparatus according to yet another feature of the invention includes a surface roughening device for roughening the surface of solder bumps of a soft solder alloy formed on a workpiece, and a surface reforming device for performing surface reforming treatment by forming a fluorine containing layer on the roughened surface of the solder bumps.
A soldering apparatus according to yet another feature of the invention is adapted to solder together a plurality of workpieces and includes a surface roughening device for roughening the surface of solder bumps of a soft solder alloy formed on one or more workpieces; a surface reforming device for performing surface reforming treatment by forming a fluorine containing layer on the roughened surface of the solder bumps; and a thermal melting unit for bringing one or more workpieces having the solder bumps that have undergone the surface roughening treatment and the surface reforming treatment into contact with other workpiece or workpieces and, in this state, performing reflow of these workpieces.
The bump forming apparatus, the presoldering treatment apparatus and the soldering apparatus described above are each capable of preventing damage to a chip, a circuit board or the like by roughening the surface of the soft solder alloy accumulated on the workpiece or the surface of the solder bumps formed on the workpiece by means of the surface roughening device so as to reduce the time required for the surface reforming treatment performed thereafter. Furthermore, as a fluorine containing layer formed as a result of surface reforming treatment by the surface reforming device improves the solder wettability and prevents re-oxidation of the surface of the solder, there is no need of flux to conduct a reflow process by the thermal melting unit, and a postprocess washing process can be eliminated accordingly, even if a soft solder alloy is used.
According to yet another feature of the invention, the surface roughening device of any one of the bump forming apparatus, the presoldering treatment apparatus and the soldering apparatus described above is a plasma exciting device adapted to roughen the surface of a soft solder alloy by means of plasma excitation, and the plasma exciting device and the surface reforming device are respectively operated in separate and different atmospheres without a pause between operation of the plasma exciting device and the operation of the surface reforming device.
The feature described above enables the conduction of the surface roughening treatment and the surface reforming treatment in separate and different atmospheres without the possibility of the two types of treatments exerting any undesirable influence on each other.
According to yet another feature of the invention, the surface roughening device of the presoldering treatment apparatus and the soldering apparatus described above is adapted to roughen the surface of the solder bumps of a soft solder alloy in a mechanical way and has an ensured reliability.
The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of a specific embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein like reference numerals in the various figures are utilized to designate like components, and wherein: